1. Field of the Invention
The present invention relates to a hot fluid generating or producing device. The fluid may be gas, such as air, or liquid, such as water.
2. Description of Related Art
A typical conventional hot fluid generating apparatus in the form of a hot air generating furnace used for heating or drying is illustrated in FIG. 11. The furnace includes a combustion chamber 73 defined within combustion chamber walls, fire tubes 75, a smoke box 74, a casing 72 and a burner 76. The burner 76 sends a flame 77 into the combustion chamber 73 and exhaust gas is exhausted to the atmosphere through an interior of each fire tube 75, the smoke box 74 and an exhaust duct connected to the smoke box 74. Combustion air is supplied by a fan 71 to an exterior of each fire tube 75 where heat of the exhaust gas is transferred to the supply air by convection and then is further heated by radiation from the flame when the supply air passes through a passage 78 between the wall of the combustion chamber 73 and the casing 72. The heated air is supplied via a duct to a thermal equipment (not shown) requiring the heated air.
However, the conventional furnace has the following problems:
1 In combustion conducted using the conventional gun-type burner, a hot spot is generated in a wall of the combustion chamber and a concentrated thermal stress is caused at the hot spot. To endure the concentrated stress, grading-up of the wall material is necessary, accompanied by an increase in cost. The reason for causing the hot spot is that a flame of the conventional gun-type burner has a non-flat temperature distribution having a peak as illustrated in FIG. 12.
2 In the furnace having the conventional gun-type burner, not only the combustion chamber (i.e., a radiation heat transfer portion) but also the fire tube portion (convective heat transfer portion) needs to be provided for obtaining a high efficiency. More particularly, in the combustion chamber of the conventional furnace, heat transfer by convection is weak because substantially no circulation of combustion gas occurs in the combustion chamber and heat transfer by radiation is also weak because a flat and high temperature distribution is not generated in the combustion chamber. Since heat of the combustion gas is not sufficiently transferred to the air flowing in the fluid passage by means of the combustion chamber only, the fire tube portion has to be provided to obtain a high rate of heat transfer. As a result, the furnace is complicated in structure and large in size, resulting in an increase in cost.